Cool idea though.
The scamming that happens to homebuyers is not even comparable to the risk in uploading docs to a website which promises they won't share user data with anyone. This is genuinely a pro buyer tool with no association with any 3rd party.
The tool has already helped many people negotiate and get a better deal on their mortgage. Please before judging understand that 70% of buyers overpay in their mortgage 1-3% in closing costs and bad rates. It's mind boggling how much lenders get away with profiting in junk fees from stressed out homebuyers.
For example, you could advise the person uploading to remove PII prior to the upload, and link to pdf editing tools that allow them to do that.
You could say that not including PII like full name(s) found on just about every loan estimate does not take away from the value of the tool.
Another thing that could be done is to provide clear means for removing any data uploaded, or opt-out pre-upload of any data being used for training.
For example by creating an account first.
Providing some skin in the game such as putting the removal behavior in the terms of service and a personal guarantee to do everything to ensure sensitivity to privacy of this information will be handled carefully staking your reputation, probably would help.